I. Field of the Invention
The present invention relates generally to torque measuring devices and, more particularly, to a torque measuring device for use with a valve actuator.
II. Description of the Prior Art
The previously known valve actuators typically comprise a housing which is mounted to a valve housing. An actuator member is rotatably mounted in the housing and mechanically connected with a valve in the valve housing so that rotation of the actuator member in a first direction simultaneously moves the valve towards its closed position. Conversely, rotation of the actuator member in the opposite direction moves the valve towards its open position.
Many of the previously known valve actuator assemblies include reversible motor means for rotatably driving the actuator motor while other actuator assemblies use only a manually operated handwheel to open and close the valve. Furthermore, many of the previously known motor driven valve actuators with motors also include a handwheel which can also be used to open and/or close the valve.
A number of the previously known valve actuators also include torque overload limit switches which are activated when the torque applied to the actuator member exceeds a predetermined amount. Typically, one switch is responsive to the torque applied to the actuator member in one rotational direction while a second switch is responsive to the torque applied to the actuator member in the opposite direction. The switches are activated in the event of a jammed valve condition and provide a signal used to deactivate the motor to prevent motor damage and/or provide an alarm signal to an operator.
One disadvantage of the previously known valve actuators with torque overload switch assemblies is that it is difficult to set or adjust the torque settings of the switch assemblies after the valve actuator has been installed in the field. An improperly adjusted switch may disadvantageously generate the torque overload signal when, in fact, no torque overload condition exists. Conversely, an improperly adjusted switch may fail to generate a torque overload signal when such a condition exists and damage not only the motor but other components of the valve actuator or the valve assembly.